Re: [ATM] Baffles

[johncdeitz@comcast.net]

Hello Nils et. al.:
We are probably splitting hairs here of course, but what else is this list for? Anyway, the reflection from the baffle is darker than the reflection from the tube in that the light is no longer grazing. As to what ASTRONOMY magizine advocates I am unsure of what you mean. I wrote the article I think you make reference to and advocate the method as outlined in Telescope Optics WITH a larger tube in the rear for maximum darkness.
Has anyone bothered to measure darkness of the paints we use? I know I have asked this before but I am hoping to stimulate someone to examine flatfields with and without baffles? 
John
 -------------- Original message ----------------------
From: "Nils Olof Carlin" <nilsolof.carlin@telia.com>
> John,
> 
> > I have taken the liberty of adding a few lines to your drawing Anthony:
> > 6f8T8MODJ.jpg
> 
> It could be found at:
> http://www.atmlist.net/contrib/johncdeitz-at-comcast-dot-net/6f8T8MODJ.JPG
> 
> 
> > in illustration of baffle method by drawing.
> 
> Judging from your drawing, you shade the lowest (nearest primary) part of 
> the tube by baffling. I claim that this part cannot be illuminated by 
> reflection via the primary and thus contribute a strong grazing reflection.
> 
> It can, of course, be illuminated directly through the tube opening, and be 
> potentially visible via the secondary by "back-scatter", but so is the 
> baffle! - and baffling for this purpose is thus meaningless. With a 
> refractor, it can be meaningful since what you see from the eyepiece is the 
> shadow side of the baffle, not the illuminated side as in a Newtonian.
> 
> Your method is appropriate for a refractor.  As I recall vaguely, Astronomy 
> magazine advocates the same principle for a Newtonian, and so did Rich 
> Coombs on a webpage that I haven't been able to locate with Google.
> 
> However, I claim (and I understand Anthony agrees here) that this is not 
> appropriate for a reflector.
> 
> regards,
> 
> Nils Olof
> 
> 
> One proceeds by 1) sketch a line from edge of tube to edge of mirror nearest 
> 2)another line from "far" limit of field 3) the intersection of these two 
> lines is baffle nearest primary. This results in more baffles and the first 
> (nearest primary) being considerable closer than in original sketch. See Pg 
> 222 Telescope Optics, 1988.
> > John Deitz
> 
> 


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